Linear motor with magnet rail support, end effect cogging reduction, and segmented armature

ABSTRACT

A linear motor is provided which includes members for engaging a magnet rail to prevent bending of the magnet rail. Such members may include a wheel or sliding block, for example. The members exert a force proximate an upper edge of the magnet rail to counter potential bending of the magnet rail during operation of the motor, and thereby avoid substantial variations in the air gaps. Furthermore, an armature yoke is provided which includes at least one partial tooth at one end of the armature yoke for reducing an end effect cogging of the linear motor armature in relation to a magnet rail along which the armature will run. In addition, an armature yoke is provided which includes multiple segments which are held end-to-end via fasteners. Such fasteners may serve as part of the magnetic flux path. A support strip may be provided to reduce bowing.

TECHNICAL FIELD

The present invention relates generally to linear motors, and moreparticularly to a linear motor which offers improved performance andmanufacturabilty.

BACKGROUND OF THE INVENTION

Linear motors are known in the art. According to a typicalconfiguration, the linear motor includes an armature which makes up thestator. The armature includes a yoke made up of a pack of ferromagneticlaminations. The yoke includes a plurality of teeth arranged at apredefined pitch, with a plurality of slots respectively separating theteeth. The armature further includes coil windings wound around theteeth and housed in the respective slots.

The linear motor also includes a magnet rail which forms the rotor. Themagnet rail includes a plurality of plate-like permanent magnets. Themagnets are positioned linearly along the rail at a predefined pitchwith corresponding gaps therebetween. The armature travels along thelength of the magnet rail with the teeth of the armature adjacent themagnets. The position of the armature is determined via a sensor, and acontroller controls the current provided to the coil windings based onthe armature position. In this manner, the armature may be selectivelydriven back and forth along the magnet rail. See, e.g., U.S. Pat. No.5,642,013.

One particular type of linear motor is known as a double-sided linearmotor. In a double-sided linear motor, the armature includes a pair ofyokes symmetrically disposed on opposite sides of the magnet rail. Eachyoke includes its own set of coil windings. The windings of both yokesare driven so as to increase the amount of force available from thelinear motor as compared to a more conventional single yoke armature.See, e.g., U.S. Pat. No. 4,868,431.

Linear motors such as those described above are quite useful in avariety of applications. These applications include, but are not limitedto, control systems, manufacturing processes, robotics, etc. Linearmotors provide precision linear movement in a whole host ofapplications.

Despite the recognized advantages associated with known linear motors,there have been a number of drawbacks. For example, it is desirable thatthe double-sided linear motor maintain an air gap of approximately equaldimension between the yoke and the magnet rail on each side of themagnet rail. Failure to provide such equal airgap results in unevenmagnetic forces being exerted on the magnet rail. In the case of arelatively thin magnet rail, this can result in a bending of the railwhich further exacerbates uneveness in the air gap and the magneticforces exerted on the magnet rail by the respective yokes.

Still another drawback associated with linear motors is “cogging”.Linear motors have a cogging or detent force that is created by theinteraction between the permanent magnets on the magnet rail and themagnetic iron forming the teeth of the armature yoke. Such coggingoccurs even when the windings are not energized. Cogging typicallyoccurs at a frequency that is determined by the number of slots perNorth-South permanent magnet cycle on the magnet rail. There typicallyare several cycles of this cogging in one North or South magnet polecycle.

In addition, because the armature in linear motors is not infinitelylong it has magnetic ends (in the direction of travel). The magneticfield at the ends of the armature is different from the magnetic fieldat the interior of the armature. This difference in magnetic fieldscauses a second cogging or detent force, referred to herein a “endeffect cogging”. End effect cogging does not exist in a rotary motorbecause rotary motors do not have a magnetic end as will be appreciated.

In general, cogging forces introduce disturbance forces into theoperation of linear motors. There have been several approaches in thepast for reducing such cogging forces. See, e.g., U.S. Pat. Nos.4,638,192, 4,912,746, 5,744,879 and 5,910,691. However, these approacheshave met with only varying degrees of success. Moreover, theseapproaches oftentimes require significant modifications to both ends ofthe armature which leads to undesirable complexity, increasedmanufacturing costs, etc.

Yet another drawback with conventional linear motors is complexityassociated with manufacture. The size and length of the armature, forexample, is dependent upon the particular application of the motor, thedesired force, etc. From the point of view of the manufacturer, this canresult in the frequent need to custom manufacture an armature.Alternatively, the manufacturer may need to keep in stock a variety ofdifferent size and length armatures.

In view of the aforementioned drawbacks associated with conventionallinear motors, it will be appreciated that there is a strong need in theart for a linear motor and method for designing the same which overcomessuch drawbacks. More particularly, there is a strong need in the art fora double-sided linear motor which is less susceptible to uneven air gapsand/or bending of the magnet rail. Moreover, there is a strong need inthe art for a linear motor that is less susceptible to the detrimentaleffects of cogging, and particularly those of end-cogging. Furthermore,there is a strong need in the art for a linear motor that is readily andefficiently manufacturable in different lengths without requiringcomplete custom design.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a double-sided linear motor isprovided. The double-sided linear motor includes a magnet railcomprising a plurality of permanent magnets arranged along a length ofthe magnet rail, a lower edge of the magnet rail being secured to abase; an armature comprising a first armature yoke and a second armatureyoke each including a plurality of teeth separated by slots, and coilwindings within the slots which are energized during operation of themotor; a motor support carriage for supporting the first armature yokeand the second armature yoke on respective sides of the magnet rail witha predefined air gap between the teeth of the first and second armatureyokes and the respective sides of the magnet rail, and permitting thearmature to move along the length of the magnet rail during operation ofthe motor; and at least one engaging member mounted to the motor supportcarriage for exerting a force proximate an upper edge of the magnet railto counter potential bending of the magnet rail during operation of themotor and thereby avoid substantial variations in at least one of theair gaps.

According to another aspect of the invention, a linear motor armature isprovided. The linear motor armature includes an armature yoke includingN teeth separated by slots, where N is an integer, and coil windingswithin the slots which are energized during operation of the motor; andwherein the armature yoke further includes at least one partial tooth atone end of the armature yoke for reducing an end effect cogging of thelinear motor armature in relation to a magnet rail along which thearmature will run, and does not include any partial teeth at the otherend of the armature yoke.

In accordance with yet another aspect of the invention, a linear motorarmature yoke is provided. The linear motor armature yoke includes aplurality of discrete yoke segments each including a plurality of teethand a plurality of slots in which coil windings will be wound; andfasteners which hold the yoke segments together end-to-end within thearmature yoke.

According to another aspect of the invention, a linear armature yoke isprovided which includes a relatively long yoke having a front facecomprising a plurality of slots for receiving armature windings, a rearface and two side faces; and at least one thin support strip secured toone of the side faces to reduce bowing along the length of the yoke.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrativeembodiments of the invention. These embodiments are indicative, however,of but a few of the various ways in which the principles of theinvention may be employed. Other objects, advantages and novel featuresof the invention will become apparent from the following detaileddescription of the invention when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of an “ideal” double-sided linearmotor;

FIG. 2 is a schematic side view of a magnetic rail included in thedouble-side linear motor of FIG. 1;

FIG. 3 is a schematic cross section of the double-sided linear motor ofFIG. 1 experiencing a bending of the magnet rail;

FIG. 4 is a perspective view, shown in partial cutaway, of adouble-sided linear motor in accordance with the present invention;

FIG. 5 is a side view in partial cutaway of the linear motor of FIG. 4shown in accordance with the present invention;

FIG. 6 is a cross-sectional view of the linear motor of FIG. 5 as takenalong line 6-6;

FIG. 7 is a cross-sectional view of the linear motor of FIG. 5 as takenalong line 7-7;

FIG. 8 is a cross-sectional view of the linear motor of FIG. 5 as takenalong line 8-8;

FIG. 9 is a cross-sectional view in relevant portion of an alternateembodiment of the linear motor in accordance with the present invention;

FIG. 10 is a top view of an armature yoke for a linear motor withreduced end effect cogging in accordance with the present invention;

FIG. 11 is a front view of the armature yoke of FIG. 9;

FIG. 12 is an end view of the armature yoke of FIG. 9;

FIG. 13 is a schematic side view of an armature yoke with discretesegments for a linear motor in accordance with the present invention;and

FIG. 14 is a schematic bottom view of an armature yoke with discretesegments for a linear motor in accordance with another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout.

Referring initially to FIG. 1, a cross-section of a double-sided linearmotor 20 is shown schematically. The motor 20 includes an armature 22made up of armature yokes 22 a and 22 b. Each armature yoke 22 a, 22 bincludes a set of coil windings 24 wound between teeth of the respectiveyokes. The armature yokes 22 a, 22 b are positioned on opposite sides ofa magnet rail 26 by a motor support carriage (not shown). Ideally, theteeth of the armature yokes 22 a, 22 b are separated from the magnetrail 26 by a predetermined air gap “ag” on each side.

FIG. 2 is a side view of the magnet rail 26. As shown, the magnet rail26 includes a plurality of plate-like permanent magnets 28. The magnets28 are positioned linearly along the rail 26 at a predefined pitch withcorresponding gaps 30 therebetween. The magnet rail 26 may be made ofmolded or machined plastic, fiberglass, metal or the like, with thepermanent magnets 28 molded, glued, or otherwise retained therein. Themagnet rail 26 is supported by virtue of its lower edge being held is abase member 32. The upper edge of the rail 26 is generally unsupported.

During operation, the armature 22 travels along the length of the magnetrail 26 with the teeth of the armature yokes 22 a, 22 b adjacent themagnets 28. As is known, current is applied to the coil windings withinthe armature 22 based on the relative position of the armature teeth tothe permanent magnets 28. A traveling magnetic wave is created whichpropels the armature 22 along the length of the magnet rail 26.

As previously mentioned, it is desirable that the double-sided linearmotor 20 maintain the air gap ag of approximately equal dimensionbetween the yoke 22 a, 22 b and the magnet rail 26 on each side of themagnet rail 26. Failure to provide such approximately equal air gap agcan result in uneven magnetic forces being exerted on the magnet rail26. In the case of a relatively thin magnet rail 26, this can result ina bending of the rail 26 as is shown in FIG. 3. Such bending of the rail26 further exacerbates any uneveness in the air gaps and the magneticforces exerted on the magnet rail 26 by the respective yokes 22 a, 22 b.

Furthermore, simple wear and tear on the motor 20 can cause the magnetrail 26 to weaken structurally and thus result in such bending of therail. In either event, the uneveness in the air gaps is furtherexacerbated by the resultant uneven magnetic forces. This can lead toproblems with motor efficiency, restricted movement of the armature,etc.

The linear motor of the present invention avoids such problemsassociated with bending of the magnet rail. More specifically, thelinear motor of the present invention provides a mechanism by which theupper edge of the magnet rail is supported. As a result, the air gapsbetween the armature yokes and the magnet rail are maintained. Thus, themotor can operate with better efficiency, increased lifespan, etc.

Referring now to FIG. 4, a double-sided linear motor 40 is shown inaccordance with one embodiment of the present invention. Although onlyone side of the motor 40 is shown in FIG. 4, it will be appreciated thatthe opposite side is generally a mirror image. The motor 40 includes anarmature 42 made up of a first armature yoke 42 a and a second armatureyoke 42 b (not shown in FIG. 4) which is generally a mirror image of thefirst armature yoke 42 a. As is conventional, each armature yoke 42 a,42 b includes a plurality of teeth arranged side-by-side with slotstherebetween. In addition, each armature yoke 42 a, 42 b includes coilwindings within the slots which are energized during operation of themotor 40.

The motor 40 further includes a motor support carriage 44 for supportingthe armature yokes 42 a, 42 b on respective sides of a magnet rail 46with a predefined air gap between the teeth of the armature yokes 42 a,42 b and the respective sides of the magnet rail 46. The motor supportcarriage 44 includes a motor support yoke 48 which supports the armatureyokes 42 a, 42 b. In addition, the motor support carriage 44 includes asupport car 50 at one end of the armature 42 for supporting one end ofthe motor support yoke 48, and a support car 52 at the other end of thearmature 42 for supporting the other end of the motor support yoke 48.

As will be described in more detail below in relation to FIGS. 5-8, thesupport cars 50, 52 each include a set of wheels, e.g., six or virtuallyany other number of wheels, which facilitate movement of the armature 42along the length of the magnet rail 46. More specifically, the magnetrail 46 is housed within a housing 54. Along the center of a base 56 ofthe housing 54, a slot 58 is provided. The lower edge of the magnet rail46 is inserted into the slot 58 and secured, and thus is supported atits lower edge by the base 56. The housing 54 may be made out of anextruded, non-ferromagnetic material such as aluminum, plastic, etc. Themagnet rail 46 is preferably molded or machined out of plastic,fiberglass, metal, or the like, and includes permanent magnets 60 spacedalong the length of the magnet rail 46 as is conventional in linearmotors. In the present example, there is only a single row of magnets 60along the length of the magnet rail 46. Thus, the same magnet 60 servesas a magnet to the armatures 42 a, 42 b on both sides of the magnet rail46. In another embodiment, however, the magnet rail 46 may include tworows of magnets 60 (i.e., one on each side of the magnet rail 46). Inthe case of a single row of magnets 60, though, the present inventionhas particular utility in the sense that the magnet rail 46 is typicallythinner and has less structural rigidity. Thus, the present invention'sability to avoid bending of the magnet rail 46 is particularlybeneficial.

The aforementioned wheels of the support cars 50, 52 are designed toride along channels on the inner walls of the housing 54. In thismanner, the armature 42 is permitted to move freely in either directiondirectly along the length of the magnet rail 46. The top of the housing54 includes a slot 62 which runs parallel with the magnet rail 46 andthrough which an arm of the motor support carriage 44 extends. Amounting plate 66 is secured to the motor support carriage 44 via a setof bolts 68 or the like. During operation, current is provided to thecoil windings of the armature yokes 42 a, 42 b in conventional fashion.This causes a traveling magnetic wave to be established between thearmature 42 and the magnet rail 46, thus propelling the armature 42together with the motor support carriage 44 along the magnet rail 46.The particular direction of travel will of course depend on the phasingof the current, etc. A physical load (not shown) coupled to the mountingplate 66 can thereby be moved in a linear direction along the length ofthe rail 46.

FIG. 5 provides a side view of the linear motor 40. Again, it will beappreciated that the linear motor 40 on the opposite side of the magnetrail 46 is basically a mirror image. As is best shown in FIG. 8, themotor support carriage 44 includes a Y-shaped motor support yoke 48which supports the armature yokes 42 a, 42 b. The motor support yoke 48straddles the magnet rail 46 such that the teeth and coil windings 70 ofthe armature yokes 42 a, 42 b are a distance ag corresponding to thedesired air gap away from the sides of the magnet rail 46.

The motor support cars 50, 52 each include a Y-shaped support car yoke72. As is best shown in FIG. 6, the support car yoke 72 also straddlesthe magnet rail 46. The support car yoke 72 includes a lower wheel 74rotatably mounted (e.g., via an axle 76 and bearings 77) on each of thesides of the yoke 72. The lower wheels 74 are designed to travel along arespective channel on the inside surface of the base 56 of the housing54. In addition, the support car yoke 72 also includes an upper wheel 78rotatably mounted on each of the sides of the yoke 72. The upper wheels78 are designed to travel along a respective channel on an upperinterior surface 80 of the housing 54. The spacing between the lowerwheels 74 and the upper wheels 78 on each yoke 72 is designed such thatvertical movement of the yoke 72 is precluded, while the wheels 74, 78provide smooth movement in a direction along the length of the magnetrail 46.

The motor support cars 50, 52 each further includes a horizontal supportstrut 80 on each side of the magnet rail 46 which couples the supportcar yoke 72 to the respective end of the motor support yoke 48. Thus,the motor support yoke 48 is supported by and carried along the lengthof the magnet rail 46 via the support cars 50, 52 and their wheels 74,78. The support cars 50, 52 along with the motor support yoke 48 may bemade of any suitable material such as machined aluminum, etc.

Referring now to FIG. 7, it is shown that the bottom surface of thestruts 80 of each of the support cars 50, 52 includes a laterallydisposed wheel 84. The wheels 84 are each rotatably mounted to the strut80 via an axle 76 and bearings 77, or the like. The wheels 84 aredesigned to travel along a respective channel on an inner side surface86 of the housing 54. The spacing between the wheels 84 is selected soas to prevent lateral movement of the motor support cars 50, 52 (i.e.,movement in a direction perpendicular to the length of the magnet rail46. At the same time, the wheels 84 permit the support cars 50, 52 aswell as the armature 42 as a whole to move freely through the housing 54along the length of the magnet rail 46.

Continuing to refer to FIG. 7, the top surface of the struts 80 of eachof the support cars 50, 52 includes a rail support wheel 90. As is bestshown in FIGS. 5 and 7, the rail support wheels 90 are rotatably mountedto the struts 80 via an axle 76 and bearings 77, or the like. The railsupport wheels 90 of each of the support cars 50, 52 are positioned soas to engage or lightly “pinch” opposite sides of the magnet rail 46near the upper edge of the magnet rail 46. As is shown in FIG. 7, theupper edge of the magnet rail 46 may include a cap 96 made of aluminumor the like. The rail support wheels 90 roll freely along the cap 96 asthe motor support carriage 44 moves along the length of the magnet rail46 during operation.

As is shown in FIG. 7, the rail support wheels 90 each engage oppositesides of the magnet rail 46. The spacing between the rail support wheels90 is approximately the same as the width of the magnet rail along thecap 96. The diameter of the wheels 90 is selected so as to provide thedesired air gap ag between the magnet rail 46 and the armature yokes 42a, 42 b. In this manner, the rail support wheels 90 can roll freelyalong the cap 96. At the same time, if the magnet rail 46 was to attemptto bend as otherwise discussed above in relation to FIG. 3, the railsupport wheel 90 towards which the magnet rail 46 attempted to bendwould exert a force on the side of the magnet rail 46 to prevent suchbending. Therefore, the air gap ag between the magnet rail 46 and thearmature yokes 42 a, 42 b on each side of the magnet rail 46 may bereliably maintained.

Thus, regardless of whether the magnet rail 46 may otherwise attempt tobend due to uneven magnetic forces from the armature 42 and/or fatigueof the magnetic rail 46, the rail support wheels 90 support the upperedge of the magnet rail 46 to prevent such bending. The rail supportwheels 90 may be made out of aluminum, nylon, rubber, steel, or othermaterial as will be appreciated. Moreover, it will be appreciated thatalthough a cap 96 is provided in the exemplary embodiment, it is notnecessary to include such cap 96. The rail support wheels 90 may ridedirectly on the main surface of the magnet rail 46.

While the rail support wheels 90 are preferred due to the minimumopposition they present to movement of the armature 42, other types ofengaging members are contemplated as being within the scope of theinvention. For example, FIG. 9 illustrates an embodiment in which therail support wheels 90 are replaced by slider blocks 98. The sliderblocks 98 abut against respective sides of the magnet rail 46 and slidealong the magnet rail 46 with travel of the armature 42. The sliderblocks 98 and cap 96 may be made of nylon or some other low frictionmaterial. In addition, or in the alternative, lubricant may be providedalong the cap 96 to reduce friction. In any event, the slider blocks 98will also provide support to the magnet rail 46 so as to resist anybending of the magnet rail 46.

Referring now to FIGS. 10-12, an exemplary armature yoke 42 a is shownin accordance with the present invention. The armature yoke 42 a isdesigned to provide reduced end effect cogging. The armature yoke 42 amay make up one of the armature yokes 42 a, 42 b in the double-sidedlinear motor 40 of FIGS. 4-9. The remaining armature yoke 42 b issymmetrically generally identical (e.g., generally a mirror image) withrespect to the magnet rail 46. However, it will also be appreciated thatthe armature yoke 42 a with reduced end effect cogging has equal utilityin an otherwise conventional one-sided linear motor. The presentinvention contemplates all such arrangements.

The armature yoke 42 a in the illustrated example includes N teeth 105(where N is an integer such as N=6) separated by slots 107. The teeth105 and slots 107 are skewed at an angle, as shown. Such skewing of theteeth and slots reduces internal slot cogging as is generally known. Inthe preferred embodiment, the yoke 42 a is made up of severallaminations 109 of soft magnetic material. Although not shown in FIGS.10-12, it will be appreciated that coil windings 70 (FIG. 8) areprovided around the teeth 105 and within the slots 107 as isconventional.

The armature yoke 42 a differs from conventional yokes by virtue of itincluding one or more partial teeth 110. The partial teeth 110 are alsomade up of laminations 109. More notably, the spacing, width andgeometry of the partial teeth 110 are designed so that the portion ofthe armature yoke 42 a with the additional one or more partial teeth 110has an end effect cogging force that is approximately 180 degrees out ofphase from the end effect cogging of the armature yoke 42 a without thepartial teeth 110. The result is the end effect cogging force of theportion of the armature yoke 42 a with the additional one or morepartial teeth 110 cancels the end effect cogging force of such anarmature yoke 42 a without the additional partial teeth 110.

Analysis of the end effect cogging of the armature yoke 42 a with theadditional partial teeth 110 and without can be done empirically or viamodeling, for example. More particularly, the armature yoke 42 a may bemodeled using commercially available finite element analysis software todetermine the end effect cogging both with additional partial teeth 110and without. By selecting a spacing, width and geometry of the partialteeth 110 so that the end effect cogging force is approximately 180degrees out of phase with that of the armature 42 a without the partialteeth, the end effect cogging forces approximately cancel out.

If the amplitudes of the end effect cogging forces were equal on a perunit basis, the armature yoke 42 a would be assembled with 50% havingthe additional tooth or teeth 110, and 50% not having the additionaltooth or teeth 110. This would result in cancellation of the end effectcogging force. Typically, the end effect cogging has differentamplitudes on a per unit basis. Therefore, the armature yoke 42 a isassembled with a proportion of parts with and without the additionalteeth 110 that results in cancellation of the end effect cogging. Forexample, if the per unit end effect cogging of the armature yoke 42 aportion with the additional teeth 110 is two times the per unit endeffect cogging of the armature yoke 42 a portion without the additionalteeth 110, the armature yoke 42 a would be assembled with 33.33% of anadditional tooth 105 forming the partial tooth 110. Likewise, 67.67% ofan additional tooth 105 would be absent. This would result in the netcancellation of the end effect cogging. Because of the skewed slot 107arrangement in FIGS. 10-12, for example, the 33.33% of an additionaltooth 105 can be split into multiple partial teeth 110. An exemplaryspacing may be A, 2A and A between the edge of the armature yoke 42 aand the partial teeth 110 as shown in FIG. 10. However, other spacingsmay also provide the desired result.

Moreover, it is noted that such technique for reducing end effectcogging requires the modification of only one end of the armature yoke42 a. There are no partial teeth 110 on the other end of the armatureyoke 42 a. The cogging reduction is obtained by the addition of all theend effect cogging forces (both portions from both ends of the armatureyoke 42 a), which effectively negate each other in a significantlyreduced cogging force.

Referring to FIG. 13, an exemplary armature yoke 42 a is shown inrelation to the magnet rail 46 in accordance with another aspect of thepresent invention. The armature yoke 42 a in this embodiment is designedto provide ease and flexibility in manufacturing. The armature yoke 42 ain this embodiment is made up of a plurality of discrete segmentsfastened together end to end. By using a plurality of discrete segments,the armature yoke 42 a can easily be manufactured to a desired lengthwithout requiring the machining of a single length yoke. For example, a36-inch long armature yoke may be made from six 6-inch segmentsconnected end-to-end. A 48-inch long armature may be made from eight6-inch segments connected end-to-end. Thus, a manufacturer or suppliercan provide multiple lengths of yokes by combining different numbers ofthe same length segments, for example. This reduces the need forstocking or supplying many different sizes or lengths of yokes, thusreducing development costs, inventory costs, etc.

As is shown in FIG. 13, the armature yoke 42 a may be made up of aplurality of discrete segments (e.g., 42 a 1, 42 a 2, etc.) arrangedend-to-end. The discrete segments may be the same or different lengths.The particular number of discrete segments will depend on the desiredlength of the overall yoke 42 a and the length of the respectivesegments as will be appreciated. The yoke 42 a makes up one of thearmature yokes 42 a, 42 b in the double-sided linear motor 40 of FIGS.4-9. The remaining armature yoke 42 b is generally a mirror image.However, it will again be appreciated that the armature yoke 42 a withdiscrete segments has equal utility in an otherwise conventionalone-sided linear motor. The present invention contemplates all sucharrangements.

Each of the discrete yoke segments (e.g., 42 a 1, 42 a 2) includes aplurality of teeth 105 with slots 107 therebetween. The ends of thesegments 42 a 1, 42 a 2 each include a slot 115 into which a respectivearm 117 of an upside down T-shaped fastener 121 is inserted. The widthof the T-shaped fasteners 121 is selected so as to allow a spacing equalto that of a slot 107 between the teeth 105 of adjacent segments.

A backplate 125 is provided on a backside of the yoke 42 a. Thebackplate 125 includes bore holes 127 through which bolts 129 areinserted. The bolts 129 include threads (not shown) at their ends whichengage a threaded hoie in the respective T-shaped fasteners 121. Bytightening the bolts 129, the respective T-shaped fasteners 121 aredrawn upward towards the backplate 125 thereby tightly securing togetherthe respective ends of the yoke segments 42 a 1, 42 a 2, etc. Similarly,partial teeth 110 can be joined to what otherwise is one of the ends ofthe yoke 42 a by virtue of an additional segment 42 a 3 as is shown inFIG. 13. End fasteners 132 may be provided to secure the ends of theyoke 42 a.

Moreover, the T-shaped fasteners 121 may be made of a soft magneticmaterial. The T-shaped fasteners 121 in the preferred embodiment aremade of a soft magnetic material and are located in the back ironportion of the yoke segments within the flux path 131 that is created inthe yoke. In this manner, the fasteners 121 do not add considerably tothe size or weight of the armature yoke 42 a. Accordingly, thecombination of yoke segments and fasteners 121 provides bothmanufacturing flexibility and ease.

In a preferred embodiment, the T-shaped fasteners 121 are spaced apartfrom one another in increments of an integer number of North-Southmagnetic pole cycles. Such integer number of North-South cycles spacingis desirable as it reduces potential losses due to eddy currents whichmay otherwise be created without such integer spacing.

Although a T-shaped fastener 121 is used in the exemplary embodiment, itwill be appreciated that various other types of fasteners may also beused. The present invention contemplates any other such fasteners.

Referring briefly to FIG. 14, another embodiment of the armature yoke ofFIG. 13 is shown. FIG. 14 represents a bottom view of the armature yokewith the windings 70 schematically shown in place wound around the teeth105 and within the slots 107. In this embodiment, a thin continuoussupport strip 135 is included along each side of the discrete elements(e.g., 42 a 1, 42 a 2, etc). The support strips 135 reduce bowing whichotherwise may occur along the length of the discrete elements arrangedend-to-end.

More specifically, the discrete elements typically may be arrangedend-to-end with T-shaped fasteners 121 therebetween to a desired length.Coils 70 are then wound about the respective teeth 105 within the slots107. The discrete elements/T-shaped fasteners/windings assembly is thenset within a mold and filled, or otherwise secured in epoxy or the likeso as to secure the position of the windings. In the embodiment of FIG.13, the laminated assembly may then be secured to the backplate 125 viathe bolts 129, for example.

However, applicants have discovered that the heating and coolingassociated with such lamination and the different coefficients ofthermal expansion associated with metal and epoxy can lead to bending ofthe overall combined discrete segments. Specifically, the discreteelements (e.g., 42 a 1, 42 a 2, etc.) combined end-to-end will tend tobow either into or out of the plane of the page relative to FIG. 13, forexample.

Accordingly, the embodiment of FIG. 14 further includes the supportstrips 135 made of a continuous thin strip of metal or the like.Although thin and of relatively light weight, the width of the strips135 can be approximately equal to the height H of the armature (asrepresented in FIG. 13). The support strips 135 are combined with theaforementioned discrete elements/T-shaped fasteners/windings assembly(e.g., by being abutted along respective sides of the assembly incontact with the outer edges of the windings 70) and secured together inepoxy or the like. In such case, the width of the strip 135 providessignificant structural rigidity to the assembly which greatly reducesand/or eliminates bowing. At the same time, the thinness and relativelight weight of the strips 135 adds little cost to the armature insofaras overall mass, etc. The combined assembly, following lamination, isthen secured to the backplate 125 via the bolts 129, for example.

The support strips 135 have been described herein as having utility forpreventing bowing which may occur as a result of discrete elementscombined end-to-end. However, it will be appreciated that such supportstrips 135 are useful even with a single element armature yoke which mayotherwise be prone to bowing due to long length, etc. Moreover, althoughtwo support strips 135 (one on each side), another embodiment mayinclude only a single support strip 135 on one side. Such embodimentsare within the intended scope of the invention.

Although the invention has been shown and described with respect tocertain preferred embodiments, it is obvious that equivalents andmodifications will occur to others skilled in the art upon the readingand understanding of the specification. The present invention includesall such equivalents and modifications, and is limited only by the scopeof the following claims.

1-9. (Cancelled)
 10. A linear motor armature, comprising: an armatureyoke including N teeth separated by slots, where N is an integer, andcoil windings within the slots which are energized during operation ofthe motor; and wherein the armature yoke further comprises at least onepartial tooth at one end of the armature yoke for reducing an end effectcogging of the linear motor armature in relation to a magnet rail alongwhich the armature will run, and does not include any partial teeth atthe other end of the armature yoke.
 11. The linear motor armature ofclaim 10, wherein the armature yoke including the at least one partialtooth is made of a soft magnetic material.
 12. The linear motor armatureof claim 10, wherein an end effect cogging force of the at least onepartial tooth is approximately 180 degrees out of phase from an endeffect cogging force of the armature yoke without the at least onepartial tooth.
 13. The linear motor armature of claim 10, wherein theteeth and slots are skewed to reduce slot cogging.
 14. The linear motorarmature of claim 10, wherein the armature yoke comprises a plurality ofpartial teeth at the one end.
 15. The linear motor armature of claim 14,wherein the plurality of partial teeth are spaced apart from oneanother. 16-23. (Cancelled)
 24. A linear motor armature yoke,comprising; a relatively long yoke having a front face comprising aplurality of slots for receiving armature windings, a rear face and twoside faces; and at least one thin support strip secured to one of theside faces to reduce bowing along the length of the yoke.